The long-term goal of this renewal application is to determine how the nervous system uses kinesthetic input to control targeted limb movement. Two problems with past research in this area of motor control are: 1) researchers lack a conceptual framework from which to answer questions about kinesthetic control and 2) new experimental techniques are needed to answer these questions. The proposed experiments will empirically test a conceptual framework in which the nervous system uses kinesthetic input initially to establish and then to adjust 3 spatial and temporal movement parameters: distance, timing, and direction. These experiments will also develop 2 experimental techniques to answer questions about kinesthetic control: tendon vibration in humans and central neural recording in behaving monkeys. Four specific aims in this grant application address the need for a conceptual framework and new experimental techniques. Specific Aim 1 is to determine in human subjects whether the distance a joint rotates to a target depends on kinesthetic input about the initial joint angle. Specific Aim 2 is to determine in human subjects how kinesthetic input controls the onset timing of joint rotations in movement sequences. Specific Aim 3 is to determine in monkey subjects how kinesthetic input controls the direction of a hand movement at both the behavioral and the neural levels. Specific Aim 4 is to develop the technique of tendon vibration in human subjects so this technique can be used to activate muscle receptors in a predictable, quantitative manner. By testing this conceptual framework and by developing these experimental techniques, we can begin to answer some fundamental questions about the kinesthetic control of targeted limb movements that were previously beyond reach. These answers will provide valuable insights into more applied problems of motor control in areas such as motor development and aging, motor disorders, myoelectrical prostheses, and motor control by astronauts in outer space.